Interlocking ring-type mandrel



y 1959 F. J. FUCHS, JR

INTERLOCKING RING-TYPE MANDREL Filed July 28. 1954 2,894,558 INTERLOCKING RENG-TYPE MANDREL Francis J. Fuchs, Jr., Winston-Salem, N.C., assignor to Western Electric (Iompany, Incorporated, New York, N.Y., a corporation of New York Application July 28, 1954, Serial No. 446,313

4 Claims. (Cl. 153-63) This invention .pertains to mandrels for use in the bending of hollow bodies and more particularly to an improved articulated mandrel for supporting the interior of a rectangular wave guide who during the bending thereof.

It .is particularly necessary in the "bending of metallic wave guide tubes to maintain the interior cross-sectional dimensions thereof within extremely close tolerances, inasmuchas electromagnetic waves are propagated along such conductors in a relatively thin skin of the metal walls forming'the bore of the tubes. Consequently any mechanical imperfections of the interior surface of such tubes, such as wrinkling, scoring, .etc., will result in undesirable changes in the electromagnetic transmission characteristics ofthe tubes.

A common procedure .in the draw bending of wave guide tubes to various shapes is the use of a flexible or articulated :maudrelto support the interior of a tube :during 1116 bending thereof. Such mandrels must uni- .forrnly support the interior of the tube at all times during :the "bending .of theztube to the desired shape and :must present ;a smooth, hard surface capable of unhindered sliding movement relative to the interior surfaces of the :tube :as the latter is drawn over the mandrel. Further,

the mandrel must :be of such a construction as to permit easy removal of the mandrel from the tube at the completion of the bending operation. These requirements find their best solution in an articulated-type mandrel wherein a body portion, which supports the tube interior, comprises a number of interlocked, relatively movable sections or links. In order to furnish uniform support to the tube walls, such links must be closely spaced together and, .in the assembled mandrel, must provide an exterior configuration similar to the interior configuration of the tube to be bent yet suflicicntly smaller in dimensions to permit slidable insertion and withdrawal of the mandrel. The ideal mandrel should be mechanically-strong inorder to withstand the forces of the bending operation and should also be so arranged and constructed as to limit the movement of the links of the mandrel to the direction or directions in which the tube is to be bent.

Therefore, it is an object of the present invention to provide an improved articulated mandrel for supporting the interior-of a rectangular wave guide tube during the bending "thereof.

It is another object of this invention to provide -an articulated mandrel capable of uniformly supporting the secured together and an articulated body consisting only of a plurality of slidably interconnected, ring-like links 2,8d,558 Patented July 14, 1959 which are arranged in two adjacent parallel rows, A and B, each row being secured at one extremity thereof to one end of the rigid stem. The present invention is an improvement upon a mandrel disclosed in a co -pending application of Francis J. Fuchs, Jr., Serial No. 262,246, :filed December 18, 1951, now Patent No. 2,778,402.

Other objects and advantages of the present invention will become apparent from the following detailed description and the accompanying drawing wherein:

Fig. l is a top plan view of the mandrel showing the assembled articulated body portion and .a portion of the rigid stem;

Pig. 2 is a side elevational view of the mandrel as shown in Fig. 1;

Fig. 3 is a plan view of one side of a representative link of which the articulated body portion of the mandrel .is comprised;

Fig. 4 is a plan view of the reverse side of a representative link of row A;

Fig. 5 is a plan view of one side of a portion of one of the strips comprising the rigid stem;

Fig. 6 is a perspective view of a portion of the rigid stem as shown in Fig. 5;

Fig. 7 is a perspective view of a link of row A as shown in Fig. 4;

Fig. 8 is a perspective view of the reverse side of the portion of the strip-shown in Fig. 6, and

Fig. 9 is a perspective view of a representative link of row B.

Attention 'now is directed to the above drawing wherein like reference numerals designate the same elements throughout the several views and wherein there is 'illustrated a mandrel comprising a rigid stem, designated generally by the numeral 11, and an articulated jor flexible :body, designated generally by the numeral 12.

The stem 11, in the illustrated embodiment, is constructed of two similar strips 13 having one extremity thereof adapted "for connection to a reciprocable mandrel shaft (not shown). Each strip 13 is provided near .a second or free extremity 15 thereof with a hole 14 having a diameter equal to one-half of the larger transverse dimension of the strips 13 and extending partially therethrough. The bottom 16 of this hole provides .a bearing surface, the purpose of which will be described later. The extremity 15 of each strip 13 is semi-circular in configuration and is provided with a recess '17 extend- .ing one half of the distance between the flat sides of the strip 13 and having transversely extending walls defined by arcuate surfaces 18 which interconnect with the hole 14. The surfaces 18 have a radius of curvature equal to one-half of the larger transverse dimension of the strip '13. Both surfaces 18 have their radial centers located on the periphery of the extremity 15, one of such centers being on the longitudinal center line of the strip and the other being offset therefrom a slight amount to provide a small clearance for slidable movement between an extremity of the body 12 and the walls of the recess 17.

The body 12 consists solely of a number of ring-like links designated generally by the numeral 19, the assembled links having rectangular crosssections when viewed from the left-hand side of Fig. l or 2 and arranged in two parallel rows, A and B (Fig. 2). Each link 19 has a radius equal to that of the recesses 17 in the strips 13 and is provided with a central, transversely extending aperture 21 which has a radius equal to that of the-holes 14 in the strips 13 and which is partially blind at one extremity thereof by reasonof an occluding, arcuate disk 20. One side of each link 19 is provided with a pair .of arcuate grooves 22 which are separated one from-the other by a portion of the aperture 21, each groove having-a depth equal to one-half of the transverse thickness'o'f the link and being partially defined by arcuate Walls 23 and 24, the position of these walls being defined by arcs of two concentric circles that have their centers of curvature on the periphery of the link. The radius of curvature of the smaller circle defining thewall 23 is equal to the radius of the holes 14 and apertures 21 and the radius of the larger circle, defining the wall 24, is equal to the radius of the link 19. The wall 23, together with the portion of the peripheral surface of the link 19 between the grooves 22, defines a transversely extending arcuate tongue 26 which is sufiiciently foreashortened longitudinally to compensate for the thickness of the occluding disks 16 or 20 and thus permit the assembly described below.

The other side of each link 19 is provided with an arcuate notch 27 located diametrically opposite the grooves 22 and the tongue 26 and extending transversely of the link for a depth equal to one-half the thickness of the link. The notch 27 is partially defined by a plane wall and by two arcuate walls 28 and 29 which interconnect with the aperture 21 and which have radii of curvature equal to that of the link 19. Each link 19 in row A has the center of curvature of the Wall 28 located at the periphery of the link and on the axis of symmetry of the notch 27. The center of curvature of the Wall 29 is located at the periphery of the link but slightly offset from the axis of symmetry of the notch 27 in order to provide clearance between the assembled links for arcuate movement therebetween. The links 19 of row B are so constructed that the positions of walls 28 and 29 are interchanged. An arcuate indentation 31 is formed in the said other side of each link 19 of row A (Figs. 4 and 7), extends transversely thereof for a distance equal to approximately one half the depth of the notih 27 and is partially defined by curved wall 32 which has a radius of curvature equal to approximately three-fourths the radius of the link 19 and a radial center coincident with that of aperture 21. Each link 19 of row B is provided with a raised arcuate shoulder 33 (Fig. 9) which is complementary to the indentations 31 of the links 19 of row A.

The mandrel is assembled by first interlocking all of the A links to form row A and the B links to form row B. This is effected by placing in the arcuate grooves 22 of a first A link a portion of a second A link in such a manner that the tongue 26 of the first link fits into the central aperture 21 of the second link and abuts against the disk 20 thereof. Additional A links are assembled in this manner until row A is of the desired length. The B links are assembled in a similar manner to form row B of the same length as row A. The extremity 15 of one strip 13 is then positioned Within the arcurate grooves 22 of an end link 19 whereby the tongue 26 of the end link 19 is positioned within the hole 14 of the said one strip 13 and abuts the bottom 16 of the hole 14, thereby attaching a row of interlocked links to the said one strip 13 and forming a first sub-assembly. The other row of interlocked rings is then attached to the other strip 13 in a similar fashion to form a second subassembly and the sub-assemblies are then placed in backto-back contacting relationship so that the shoulders 33 of the links 19 in row B are slidably positioned within the complementary indentations 31 of the links 19 in row A. The two strips 13 are then secured together, for example, by means of dowels 34 in apertures 35 to form the unitary rigid mandrel stem 11. In this assembled relationship, each row of links maintains the nested relationship of the links of the other row, hence no other securing means is required. The provision of the interlocking shoulders 33 and indentations 31 prevents relative longitudinal movement between rows A and B, hence tends to retain the articulated body 12 in the desired form and thus results in more accurate bends. The disks 20and the bottoms 16 of the holes 14 provide bearing surfaces for the extremities of the tongues 26 and tend to prevent any deformation of the body 12 due to lateral forces which may be exerted upon the mandrel during the bending operation.

This mandrel combines the advantages of the strength and rigidity necessary to effect an accurate bend in a tube with ease of assembly and disassembly to increase or decrease the length of the body 12 as may be required when bending tubes of different lengths. Thus the mandrel can be lengthened or shortened simply by loosening the strips 13, adding or removing one or more links 19 and then retightening the strips 13.

Further, this mandrel can bend in two directions from its longitudinal axis. This feature is desirable in making compound bends in tubes.

It is to be understood that various additions or modifications could be made to the embodiment disclosed herein without departing from the spirit and scope of the present invention.

What is claimed is:

1. A mandrel which comprises a stem and a flexible body having one end attached to the stem, the flexible body including two interlocked rows of interconnected circular links having central apertures, the outer side of each link having a pair of arcuate grooves and a tongue, the inner side of each link in one row having an arcuate notch diametrically opposite the tongue and an arcuate indentation opposite the tongue, the inner side of each link in the other row having an arcuate notch diametrically opposite the tongue and an arcuate shoulder opposite the tongue, in each row the tongues of the links being fitted into the central apertures of adjacent links and the portions of the links adjacent the notches being fitted into the grooves of adjacent links, the arcuate recesses of the links of the one row slidably receiving the arcuate shoulders of the links of the other row such that the two rows are interlocked.

2. A mandrel which comprises a stem and a flexible body having one end attached to the stem, the flexible body including two interlocked rows of interconnected circular links having central apertures, the outer side of each link having a pair of arcuate grooves and a tongue, the inner side of each link having an arcuate notch diametrically opposite the tongue, in each row the tongues of the links being fitted into the central apertures of adjacent links and portions of the links adjacent the notches being fitted into the grooves of adjacent links, the inner sides of the links of one row having engaging means formed thereon, the inner sides of the links of the other row having means complementary to the engaging means and coupled thereto such that the two rows are interlocked.

3. A mandrel which comprises a stem and a flexible body having one end attached to the stem, the flexible body including two interlocked rows of interconnected circular links having central apertures, the outer side of each link having a pair of arcuate grooves, a tongue, and a disk partially occluding the aperture, the inner side of each link having an arcuate notch diametrically opposite the tongue, in each row the tongues of the links being fitted into the central apertures of adjacent links, the terminal faces of the tongues bearing in frictional contact with the inner faces of the disks and portions of the links adjacent the notches being fitted into the grooves of adjacent links, the inner sides of the links of one row having engaging means formed thereon, and the inner sides of the links of the other row having means complementary to the engaging means and coupled thereto such that the two rows are interlocked.

4. A mandrel which comprises a stem and a flexible body having one end attached to the stem, the flexible body including two interlocked rows of interconnected circular links having central apertures, the outer side of each link having a pair of arcuate grooves, a tongue, and a disk partially occluding the aperture, the inner side of each link in one row having an arcuate notch diametrically opposite the tongue and an arcuate indentation 5 6 opposite the tongue, the inner side of each link in the References Cited in the file of this patent other row having an arcuate notch diametrically opposite the tongue and an arcuate shoulder opposite the UNITED STATES PATENTS tongue, in each row the tongues of the links being fitted 1,021,450 Cox Mar. 26, 1912 into the central apertures of adjacent links, the terminal 5 1,181,170 Rylen May 2, 1916 faces of the tongues bearing in frictional contact with 1,683,573 Mueller et al Sept. 4, 1928 the disks and the portions of the links adjacent the 2,778,402 Fuchs Jan. 22, 1957 notches being fitted into the grooves of adjacent links, the arcuate recesses of the links of the one row slidably FOREIGN PATENTS receiving the arcuate shoulders of the links of the other 10 5, 19 Great Britain of 1885 row such that the two rows are interlocked. 

